Size plays a key role in miniaturization and automation, where smaller is usually better. Conventional electromagnetic motors have certain restrictions when it comes to reducing dimensions while maintaining accuracy and high efficiency of motion along with reduced energy consumption. This gap can be addressed by Piezo ceramic inertia motors, also known as stick-slip motors. These miniature direct-drive mechanisms can be integrated in highly precise goniometer cradles, rotary stages, linear positioners and even 6-axis parallel positioning systems. Besides inertia-type motors, there are many other types of piezo motors such as high-force piezo-walk drives and high-speed ultrasonic drives.

Q-motion miniature linear and rotary stages are available in single or multi-axis combinations. Their operating principle is based on the piezo inertia (stick-slip) effect.

Stick-slip motors are particularly economical and can offer nanometer precision motion, if desired. These motors offer the best force/size ratio for smallest dimensions.

Working Principle

A piezoelectric ceramic actuator is preloaded against a moving runner. A drive signal with a quasi saw-tooth shape controls the actuator, which expands slowly and contracts rapidly (or in the opposite direction). During the rapid contraction, the coupling element slips along the runner, which generally remains in place, whereas during the slow expansion, the runner sticks to the coupling element and moves along.

Q-motion piezo inertia motors are extremely small. They allow the design of nanometer-precision mechanisms with scaled-down dimensions that were unthinkable a few years ago – ideal for integration into miniaturized instrumentation.

There are two different versions that were developed and optimized either for moderate force, miniature size or higher force and compact size.

Tangential Inertia Drive Motor.

To 2 N Holding Force

Very Small Dimensions

Simple Mechanics

Watch Stick-Slip Working Principle Video.

Mini-Rod Inertia Drive Motor

Mini-Rod piezo inertia motor drives are based on an actuator moving a small rod – or moving along the rod when the rod is fixed. With up to 10 N pushing/holding force, these motors are more powerful than the tangential drives. They can be incorporated into linear positioning stages and linear actuators, although the principle does not apply to rotary stages.

Train of 6 nm steps executed with Q-545 closed-loop stage, measured with laser interferometer at 5 kHz sampling rate. The highest encoder resolution is 1 nm. This type of resolution allows applications in high resolution microscopy. The LPS-45, a predecessor of the Q-545, was used for nanometer precise accurate positioning of the Fresnel Zone Plate along the optical axis of a compact stand-alone EUV microscope. (Image: PI)

The runner is moved in the defined direction during the stick phase, while it does not move during the slip phase. The so-called back-stepping effect causes a slight backward motion during the acceleration phase of the piezo actuator.

Self-Locking at Rest

Similar to most piezo motors, Q-Motion inertia drives are self-locking at rest. There is no position dither, no heat dissipation and no power consumption.

Velocity Control

Back-stepping Effect

Between each slip cycle and stick, a miniscule position shift known as the back-stepping effect can be observed. This effect is inseparably connected with the inertia drive principle and its relevance relies on the application.

A backstepping effect is too minute to be noticed at a data sample rate of 133 kHz. As a result, PI states that the back-stepping effect does not affect the smoothness and constancy of velocity, but there are other factors that influence the velocity directly.

Constancy of Velocity at a Microscopic Level

Using the entry level E-871.1A1 motion controller, the chosen velocity is attained by adjusting the operating frequency. Adjusting the frequency means the voltage profile of a single step continues to be constant with pauses in between. More advanced velocity control is provided by the E-873 controller.

Simplified control voltage profile for different operating frequencies.

Optional digital joystick for manual operation a single channel version is available as the E-871

E-870 Driver

Features of the E-870 driver include:

Host Software LabVIEW Driver Included

With Digital USB interface

One to Four Actuators, Serial Control (through demultiplexing)

Ideal for OEM Applications

For PIShift and PiezoMike Piezo Inertia Drives

E-872 OEM Driver

Features of the E-472.02 OEM and E-872.01 driver are:

Cost Effective

E-872.02: Micro Step Modus

E-872.01: Full Step Modus

Step-Direction Input Signal

E-873 Macro

The E-873 Macro programmable specifications comprise of:

Data Recorder

Compatible Sub-D Connectors for Q-Motion Stages

Velocity Control

Joystick Input for Manual Operation

Interfaces: TCP/ IP, RS-232 , and USB

ID Chip Support

Digital I/ O Ports (TTL)

Optionally Available with Metal-Sheet Housing for OEM Applications

Vacuum and Nonmagnetic Operation

High-Vacuum to 10-6 hPa

Unprepared and standard Q-Motion stages can be employed in ambient conditions and for vacuum up to 10-6 hPa. The C-815.VF vacuum feedthrough is available for vacuum operation.

On the air side, the following cables will be available for linking the feedthrough with the E-873 controller (plus adapter cable for E-871, which is included in the delivery of the stage):

Description

E-873.UHV1

Air-Side Adapter Cable, Sub-D 15, 1 m

C-815.VF

Vacuum Feedthrough, Sub-D 15

These air-side cables are also used for the feedthrough for UHV.

Ultrahigh Vacuum to 10-9 hPa

Ultrahigh vacuum models are also available.

Description

C-815.VFU3

Vacuum Feedthrough, compatible to 10-9 hPa, 3x Sub-D 15

E-873.UHV2

Air-Side Adapter Cable, Sub-D 15, 2 m

Nonmagnetic Operation

At present, PI is evaluating ceramic bearings for nonmagnetic stage designs. Nonmagnetic operation is of interest in the environment of electron beam imaging such as lithography or microscopy.

Tests in High Magnetic Fields

The Karlsruhe Institute of Technology (KIT) has carried out tests in high magnetic fields of 9.4 Tesla (T). The stage (not operating) was not attracted by the magnetic field and hence was not magnetized.

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